The present invention relates to a process for the preparation of a protein of interest in the milk of a transgenic animal. It also relates to the constructs which make it possible to obtain these animals, the animals obtained as well as the cells containing the constructs which permit the expression of a heterologous protein.
Several routes have been pursued in order to obtain proteins of biological, therapeutic or industrial interest, and which are naturally produced in small quantities or in a form difficult to purify.
It has thus been possible to produce proteins using genetic recombination techniques, by microorganisms such as bacteria or yeasts. Nevertheless, most of the proteins require, after their synthesis, a maturation stage consisting in chemical modifications of certain reacting groups, glycosylation, and the like. Prokaryotic cells do not have the adequate enzymatic content for carrying out this maturation, hence the production of inactive proteins and/or proteins with high antigenicity.
It is therefore preferable to synthesize these proteins in eukaryotic cells, which will perform the appropriate enzymatic conversions. Nevertheless, the large-scale culture of tissue cells poses a number of technical and economical difficulties.
Another approach therefore consists in causing these proteins to be produced by cells in vivo, using transgenic animals. It is desirable that the system used permits the production of proteins in large quantities and which are easily recoverable. It is therefore advantageous that the recombinant protein is produced in the mammary gland of transgenic animals, and excreted in the milk. It is indeed a biological fluid which can be easily collected, having a relatively limited complexity and a low proteolytic activity; in addition, the processes of maturation of the recombinant proteins will be probably ensured (glycosylation, phosphorylation, cleavage and the like).